1. Field of the Invention
This invention concerns a synthetic polyamide filament which is dyeable both with acid and with basic dyes. More particularly, it concerns a filament having a selectively acid-dyeable polyamide core surrounded by a basic-dyeable polyamide sheath. Such filaments provide unusual dye styling possibilities in the combination with other acid and basic-dyeable monocomponent polyamide filaments.
2. Description of the Prior Art
For styling purposes, the acid dyeability of polyamide filaments can be varied dependent upon the amine-end concentration. Basic-dyeability can be obtained by copolymerization with an amide constituent containing aromatic sulfonate groups. Polyamide filaments composed of two polyamides, one of which is free of sulfonate groups and the other of which contains basic-dyeable aromatic sulfonate groups, spun in a side-by-side configuration are described in Japanese Patent Application No. 21613/72. The filaments are receptive both to acid and to basic dyes. The acid-dyeability of such filaments is dependent upon the acid-dyeable groups in the polyamide component which is free of sulfonate groups. Greater versatility in dye styling effects could be realized by a polyamide filament which is receptive both to acid and to basic dyes but which provides further selectivity between different types of acid dyes.